One thing that was done after the August attack was definitely and finally to withdraw the Vermorel sprayers for use for clearing the gas out of the trenches and dugouts. These instruments, brought up for the work of spraying fruit trees and vineyards, had done some first-class fighting of the German gas, right in the front line, as long as the gas was chlorine. But with the introduction of large quantities of phosgene the work of the sprayers was gone. They could not touch the phosgene, and consequently Tommy’s dependence on them was a snare and made things more dangerous for him than if they had not been used at all. For a dugout might be sprayed and thought, therefore, to be quite healthy to sleep in and yet contain as much phosgene as would at any rate cause minor and delayed effects. To clear out the gas recourse was had to ventilation by means of fires and by specially constructed canvas fans. These fans were the invention of an English lady named Ayrton--the widow of the physicist of that name--and were originally intended by her for fanning back the gas cloud to the German trenches. Of course they were quite incapable of doing any such thing, but during trials with them it was found that they were quite good, after an attack, for fanning the gas out of the trenches or creating such a draft of air into a dugout or cellar as to force out the impure air from the interior. These anti-gas fans, or flapper fans as they were called, are made of canvas supported by braces of cane and attached to a hickory handle about two feet long. The blade of the fan, which looks like an immense fly swat, is hinged in two places and measures about fifteen inches square. When the fan is brought down on the ground it bends over on the back hinge and produces a sharp puff of air, in just the same way that the sudden shutting of an open book does. By working the fans in series, one man behind another, it is possible to keep a current of air going which will ventilate a room or clear out a trench in remarkably quick time. In clearing out a trench the fan is brought back over the shoulder, and this helps to “shovel” the contaminated air out of the trench after it has been brought off the ground by the lower stroke, which is more like a smart slap. These fans are kept as trench stores, which means that they are handed over on relief to the incoming unit taking over the line of trenches. They have proved very useful, especially in skilful hands their chief value being that, unlike the sprayers, they do not distinguish between different kinds of gases and they will deal as unceremoniously with tear gas and phosgene as they do with chlorine.